Generally, semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Home, industrial, and automotive devices that in the past comprised only mechanical components now have electronic parts that require semiconductor devices, for example.
Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned and etched to form integrated circuits (IC's). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip.
There is a trend in the semiconductor industry towards scaling down the size of integrated circuits, to meet demands of increased performance and smaller device size. However, as semiconductor devices become smaller, it becomes more difficult to pattern material layers because of diffraction and other effects that occur during the lithography process. In particular, photolithography techniques used to pattern the various material layers become challenging as device features shrink.
Optical photolithography involves projecting or transmitting light through a pattern made of optically opaque areas and optically clear areas on a mask or reticle. As a light beam projects onto a wafer during patterning, interference of the light may be produced which can distort the shape of the desired pattern and deleteriously affect the critical dimension (CD) of the semiconductor device.
Optical proximity correction (OPC) is typically used to improve photolithography processes of semiconductor devices. One type of OPC involves using serifs on a photolithography mask to decrease corner rounding effects. Another type of mask manipulation is referred to in the art as scatter bars, which are used for improving imaging and lithographic process windows. The scatter bars comprise bar-like patterns that are formed on the photolithography mask. Scatter bars are generally smaller than the resolution limit of the lens used, and do not leave a corresponding resist image on the wafer plane.
Even with the use of such enhancement techniques, some features of semiconductor still remain unpatternable due to an effect known in the art as a “forbidden pitch.” A forbidden pitch is a distance between two adjacent features that is unpatternable at a particular wavelength and thickness of photoresist, as examples. Forbidden pitches restrict design rules and result in increased chip size.
Thus, what are needed in the art are improved lithography techniques and lithography masks that are capable of patterning features that currently are considered to have forbidden pitches.